| /* |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| /* |
| * This file is available under and governed by the GNU General Public |
| * License version 2 only, as published by the Free Software Foundation. |
| * However, the following notice accompanied the original version of this |
| * file: |
| * Written by Josh Bloch of Google Inc. and released to the public domain, |
| * as explained at http://creativecommons.org/publicdomain/zero/1.0/. |
| */ |
| |
| package java.util; |
| |
| import java.io.*; |
| import java.util.function.Consumer; |
| |
| // BEGIN android-note |
| // removed link to collections framework docs |
| // END android-note |
| |
| /** |
| * Resizable-array implementation of the {@link Deque} interface. Array |
| * deques have no capacity restrictions; they grow as necessary to support |
| * usage. They are not thread-safe; in the absence of external |
| * synchronization, they do not support concurrent access by multiple threads. |
| * Null elements are prohibited. This class is likely to be faster than |
| * {@link Stack} when used as a stack, and faster than {@link LinkedList} |
| * when used as a queue. |
| * |
| * <p>Most {@code ArrayDeque} operations run in amortized constant time. |
| * Exceptions include |
| * {@link #remove(Object) remove}, |
| * {@link #removeFirstOccurrence removeFirstOccurrence}, |
| * {@link #removeLastOccurrence removeLastOccurrence}, |
| * {@link #contains contains}, |
| * {@link #iterator iterator.remove()}, |
| * and the bulk operations, all of which run in linear time. |
| * |
| * <p>The iterators returned by this class's {@link #iterator() iterator} |
| * method are <em>fail-fast</em>: If the deque is modified at any time after |
| * the iterator is created, in any way except through the iterator's own |
| * {@code remove} method, the iterator will generally throw a {@link |
| * ConcurrentModificationException}. Thus, in the face of concurrent |
| * modification, the iterator fails quickly and cleanly, rather than risking |
| * arbitrary, non-deterministic behavior at an undetermined time in the |
| * future. |
| * |
| * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
| * as it is, generally speaking, impossible to make any hard guarantees in the |
| * presence of unsynchronized concurrent modification. Fail-fast iterators |
| * throw {@code ConcurrentModificationException} on a best-effort basis. |
| * Therefore, it would be wrong to write a program that depended on this |
| * exception for its correctness: <i>the fail-fast behavior of iterators |
| * should be used only to detect bugs.</i> |
| * |
| * <p>This class and its iterator implement all of the |
| * <em>optional</em> methods of the {@link Collection} and {@link |
| * Iterator} interfaces. |
| * |
| * @author Josh Bloch and Doug Lea |
| * @since 1.6 |
| * @param <E> the type of elements held in this collection |
| */ |
| public class ArrayDeque<E> extends AbstractCollection<E> |
| implements Deque<E>, Cloneable, java.io.Serializable |
| { |
| /** |
| * The array in which the elements of the deque are stored. |
| * The capacity of the deque is the length of this array, which is |
| * always a power of two. The array is never allowed to become |
| * full, except transiently within an addX method where it is |
| * resized (see doubleCapacity) immediately upon becoming full, |
| * thus avoiding head and tail wrapping around to equal each |
| * other. We also guarantee that all array cells not holding |
| * deque elements are always null. |
| */ |
| private transient Object[] elements; |
| |
| /** |
| * The index of the element at the head of the deque (which is the |
| * element that would be removed by remove() or pop()); or an |
| * arbitrary number equal to tail if the deque is empty. |
| */ |
| private transient int head; |
| |
| /** |
| * The index at which the next element would be added to the tail |
| * of the deque (via addLast(E), add(E), or push(E)). |
| */ |
| private transient int tail; |
| |
| /** |
| * The minimum capacity that we'll use for a newly created deque. |
| * Must be a power of 2. |
| */ |
| private static final int MIN_INITIAL_CAPACITY = 8; |
| |
| // ****** Array allocation and resizing utilities ****** |
| |
| /** |
| * Allocates empty array to hold the given number of elements. |
| * |
| * @param numElements the number of elements to hold |
| */ |
| private void allocateElements(int numElements) { |
| int initialCapacity = MIN_INITIAL_CAPACITY; |
| // Find the best power of two to hold elements. |
| // Tests "<=" because arrays aren't kept full. |
| if (numElements >= initialCapacity) { |
| initialCapacity = numElements; |
| initialCapacity |= (initialCapacity >>> 1); |
| initialCapacity |= (initialCapacity >>> 2); |
| initialCapacity |= (initialCapacity >>> 4); |
| initialCapacity |= (initialCapacity >>> 8); |
| initialCapacity |= (initialCapacity >>> 16); |
| initialCapacity++; |
| |
| if (initialCapacity < 0) // Too many elements, must back off |
| initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements |
| } |
| elements = new Object[initialCapacity]; |
| } |
| |
| /** |
| * Doubles the capacity of this deque. Call only when full, i.e., |
| * when head and tail have wrapped around to become equal. |
| */ |
| private void doubleCapacity() { |
| assert head == tail; |
| int p = head; |
| int n = elements.length; |
| int r = n - p; // number of elements to the right of p |
| int newCapacity = n << 1; |
| if (newCapacity < 0) |
| throw new IllegalStateException("Sorry, deque too big"); |
| Object[] a = new Object[newCapacity]; |
| System.arraycopy(elements, p, a, 0, r); |
| System.arraycopy(elements, 0, a, r, p); |
| elements = a; |
| head = 0; |
| tail = n; |
| } |
| |
| /** |
| * Constructs an empty array deque with an initial capacity |
| * sufficient to hold 16 elements. |
| */ |
| public ArrayDeque() { |
| elements = new Object[16]; |
| } |
| |
| /** |
| * Constructs an empty array deque with an initial capacity |
| * sufficient to hold the specified number of elements. |
| * |
| * @param numElements lower bound on initial capacity of the deque |
| */ |
| public ArrayDeque(int numElements) { |
| allocateElements(numElements); |
| } |
| |
| /** |
| * Constructs a deque containing the elements of the specified |
| * collection, in the order they are returned by the collection's |
| * iterator. (The first element returned by the collection's |
| * iterator becomes the first element, or <i>front</i> of the |
| * deque.) |
| * |
| * @param c the collection whose elements are to be placed into the deque |
| * @throws NullPointerException if the specified collection is null |
| */ |
| public ArrayDeque(Collection<? extends E> c) { |
| allocateElements(c.size()); |
| addAll(c); |
| } |
| |
| // The main insertion and extraction methods are addFirst, |
| // addLast, pollFirst, pollLast. The other methods are defined in |
| // terms of these. |
| |
| /** |
| * Inserts the specified element at the front of this deque. |
| * |
| * @param e the element to add |
| * @throws NullPointerException if the specified element is null |
| */ |
| public void addFirst(E e) { |
| if (e == null) |
| throw new NullPointerException(); |
| elements[head = (head - 1) & (elements.length - 1)] = e; |
| if (head == tail) |
| doubleCapacity(); |
| } |
| |
| /** |
| * Inserts the specified element at the end of this deque. |
| * |
| * <p>This method is equivalent to {@link #add}. |
| * |
| * @param e the element to add |
| * @throws NullPointerException if the specified element is null |
| */ |
| public void addLast(E e) { |
| if (e == null) |
| throw new NullPointerException(); |
| elements[tail] = e; |
| if ( (tail = (tail + 1) & (elements.length - 1)) == head) |
| doubleCapacity(); |
| } |
| |
| /** |
| * Inserts the specified element at the front of this deque. |
| * |
| * @param e the element to add |
| * @return {@code true} (as specified by {@link Deque#offerFirst}) |
| * @throws NullPointerException if the specified element is null |
| */ |
| public boolean offerFirst(E e) { |
| addFirst(e); |
| return true; |
| } |
| |
| /** |
| * Inserts the specified element at the end of this deque. |
| * |
| * @param e the element to add |
| * @return {@code true} (as specified by {@link Deque#offerLast}) |
| * @throws NullPointerException if the specified element is null |
| */ |
| public boolean offerLast(E e) { |
| addLast(e); |
| return true; |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E removeFirst() { |
| E x = pollFirst(); |
| if (x == null) |
| throw new NoSuchElementException(); |
| return x; |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E removeLast() { |
| E x = pollLast(); |
| if (x == null) |
| throw new NoSuchElementException(); |
| return x; |
| } |
| |
| public E pollFirst() { |
| int h = head; |
| @SuppressWarnings("unchecked") |
| E result = (E) elements[h]; |
| // Element is null if deque empty |
| if (result == null) |
| return null; |
| elements[h] = null; // Must null out slot |
| head = (h + 1) & (elements.length - 1); |
| return result; |
| } |
| |
| public E pollLast() { |
| int t = (tail - 1) & (elements.length - 1); |
| @SuppressWarnings("unchecked") |
| E result = (E) elements[t]; |
| if (result == null) |
| return null; |
| elements[t] = null; |
| tail = t; |
| return result; |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E getFirst() { |
| @SuppressWarnings("unchecked") |
| E result = (E) elements[head]; |
| if (result == null) |
| throw new NoSuchElementException(); |
| return result; |
| } |
| |
| /** |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E getLast() { |
| @SuppressWarnings("unchecked") |
| E result = (E) elements[(tail - 1) & (elements.length - 1)]; |
| if (result == null) |
| throw new NoSuchElementException(); |
| return result; |
| } |
| |
| @SuppressWarnings("unchecked") |
| public E peekFirst() { |
| // elements[head] is null if deque empty |
| return (E) elements[head]; |
| } |
| |
| @SuppressWarnings("unchecked") |
| public E peekLast() { |
| return (E) elements[(tail - 1) & (elements.length - 1)]; |
| } |
| |
| /** |
| * Removes the first occurrence of the specified element in this |
| * deque (when traversing the deque from head to tail). |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the first element {@code e} such that |
| * {@code o.equals(e)} (if such an element exists). |
| * Returns {@code true} if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * @param o element to be removed from this deque, if present |
| * @return {@code true} if the deque contained the specified element |
| */ |
| public boolean removeFirstOccurrence(Object o) { |
| if (o == null) |
| return false; |
| int mask = elements.length - 1; |
| int i = head; |
| Object x; |
| while ( (x = elements[i]) != null) { |
| if (o.equals(x)) { |
| delete(i); |
| return true; |
| } |
| i = (i + 1) & mask; |
| } |
| return false; |
| } |
| |
| /** |
| * Removes the last occurrence of the specified element in this |
| * deque (when traversing the deque from head to tail). |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the last element {@code e} such that |
| * {@code o.equals(e)} (if such an element exists). |
| * Returns {@code true} if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * @param o element to be removed from this deque, if present |
| * @return {@code true} if the deque contained the specified element |
| */ |
| public boolean removeLastOccurrence(Object o) { |
| if (o == null) |
| return false; |
| int mask = elements.length - 1; |
| int i = (tail - 1) & mask; |
| Object x; |
| while ( (x = elements[i]) != null) { |
| if (o.equals(x)) { |
| delete(i); |
| return true; |
| } |
| i = (i - 1) & mask; |
| } |
| return false; |
| } |
| |
| // *** Queue methods *** |
| |
| /** |
| * Inserts the specified element at the end of this deque. |
| * |
| * <p>This method is equivalent to {@link #addLast}. |
| * |
| * @param e the element to add |
| * @return {@code true} (as specified by {@link Collection#add}) |
| * @throws NullPointerException if the specified element is null |
| */ |
| public boolean add(E e) { |
| addLast(e); |
| return true; |
| } |
| |
| /** |
| * Inserts the specified element at the end of this deque. |
| * |
| * <p>This method is equivalent to {@link #offerLast}. |
| * |
| * @param e the element to add |
| * @return {@code true} (as specified by {@link Queue#offer}) |
| * @throws NullPointerException if the specified element is null |
| */ |
| public boolean offer(E e) { |
| return offerLast(e); |
| } |
| |
| /** |
| * Retrieves and removes the head of the queue represented by this deque. |
| * |
| * This method differs from {@link #poll poll} only in that it throws an |
| * exception if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #removeFirst}. |
| * |
| * @return the head of the queue represented by this deque |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E remove() { |
| return removeFirst(); |
| } |
| |
| /** |
| * Retrieves and removes the head of the queue represented by this deque |
| * (in other words, the first element of this deque), or returns |
| * {@code null} if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #pollFirst}. |
| * |
| * @return the head of the queue represented by this deque, or |
| * {@code null} if this deque is empty |
| */ |
| public E poll() { |
| return pollFirst(); |
| } |
| |
| /** |
| * Retrieves, but does not remove, the head of the queue represented by |
| * this deque. This method differs from {@link #peek peek} only in |
| * that it throws an exception if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #getFirst}. |
| * |
| * @return the head of the queue represented by this deque |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E element() { |
| return getFirst(); |
| } |
| |
| /** |
| * Retrieves, but does not remove, the head of the queue represented by |
| * this deque, or returns {@code null} if this deque is empty. |
| * |
| * <p>This method is equivalent to {@link #peekFirst}. |
| * |
| * @return the head of the queue represented by this deque, or |
| * {@code null} if this deque is empty |
| */ |
| public E peek() { |
| return peekFirst(); |
| } |
| |
| // *** Stack methods *** |
| |
| /** |
| * Pushes an element onto the stack represented by this deque. In other |
| * words, inserts the element at the front of this deque. |
| * |
| * <p>This method is equivalent to {@link #addFirst}. |
| * |
| * @param e the element to push |
| * @throws NullPointerException if the specified element is null |
| */ |
| public void push(E e) { |
| addFirst(e); |
| } |
| |
| /** |
| * Pops an element from the stack represented by this deque. In other |
| * words, removes and returns the first element of this deque. |
| * |
| * <p>This method is equivalent to {@link #removeFirst()}. |
| * |
| * @return the element at the front of this deque (which is the top |
| * of the stack represented by this deque) |
| * @throws NoSuchElementException {@inheritDoc} |
| */ |
| public E pop() { |
| return removeFirst(); |
| } |
| |
| private void checkInvariants() { |
| // assert elements[tail] == null; |
| // assert head == tail ? elements[head] == null : |
| // (elements[head] != null && |
| // elements[(tail - 1) & (elements.length - 1)] != null); |
| // assert elements[(head - 1) & (elements.length - 1)] == null; |
| } |
| |
| /** |
| * Removes the element at the specified position in the elements array, |
| * adjusting head and tail as necessary. This can result in motion of |
| * elements backwards or forwards in the array. |
| * |
| * <p>This method is called delete rather than remove to emphasize |
| * that its semantics differ from those of {@link List#remove(int)}. |
| * |
| * @return true if elements moved backwards |
| */ |
| private boolean delete(int i) { |
| //checkInvariants(); |
| final Object[] elements = this.elements; |
| final int mask = elements.length - 1; |
| final int h = head; |
| final int t = tail; |
| final int front = (i - h) & mask; |
| final int back = (t - i) & mask; |
| |
| // Invariant: head <= i < tail mod circularity |
| if (front >= ((t - h) & mask)) |
| throw new ConcurrentModificationException(); |
| |
| // Optimize for least element motion |
| if (front < back) { |
| if (h <= i) { |
| System.arraycopy(elements, h, elements, h + 1, front); |
| } else { // Wrap around |
| System.arraycopy(elements, 0, elements, 1, i); |
| elements[0] = elements[mask]; |
| System.arraycopy(elements, h, elements, h + 1, mask - h); |
| } |
| elements[h] = null; |
| head = (h + 1) & mask; |
| return false; |
| } else { |
| if (i < t) { // Copy the null tail as well |
| System.arraycopy(elements, i + 1, elements, i, back); |
| tail = t - 1; |
| } else { // Wrap around |
| System.arraycopy(elements, i + 1, elements, i, mask - i); |
| elements[mask] = elements[0]; |
| System.arraycopy(elements, 1, elements, 0, t); |
| tail = (t - 1) & mask; |
| } |
| return true; |
| } |
| } |
| |
| // *** Collection Methods *** |
| |
| /** |
| * Returns the number of elements in this deque. |
| * |
| * @return the number of elements in this deque |
| */ |
| public int size() { |
| return (tail - head) & (elements.length - 1); |
| } |
| |
| /** |
| * Returns {@code true} if this deque contains no elements. |
| * |
| * @return {@code true} if this deque contains no elements |
| */ |
| public boolean isEmpty() { |
| return head == tail; |
| } |
| |
| /** |
| * Returns an iterator over the elements in this deque. The elements |
| * will be ordered from first (head) to last (tail). This is the same |
| * order that elements would be dequeued (via successive calls to |
| * {@link #remove} or popped (via successive calls to {@link #pop}). |
| * |
| * @return an iterator over the elements in this deque |
| */ |
| public Iterator<E> iterator() { |
| return new DeqIterator(); |
| } |
| |
| public Iterator<E> descendingIterator() { |
| return new DescendingIterator(); |
| } |
| |
| private class DeqIterator implements Iterator<E> { |
| /** |
| * Index of element to be returned by subsequent call to next. |
| */ |
| private int cursor = head; |
| |
| /** |
| * Tail recorded at construction (also in remove), to stop |
| * iterator and also to check for comodification. |
| */ |
| private int fence = tail; |
| |
| /** |
| * Index of element returned by most recent call to next. |
| * Reset to -1 if element is deleted by a call to remove. |
| */ |
| private int lastRet = -1; |
| |
| public boolean hasNext() { |
| return cursor != fence; |
| } |
| |
| public E next() { |
| if (cursor == fence) |
| throw new NoSuchElementException(); |
| @SuppressWarnings("unchecked") |
| E result = (E) elements[cursor]; |
| // This check doesn't catch all possible comodifications, |
| // but does catch the ones that corrupt traversal |
| if (tail != fence || result == null) |
| throw new ConcurrentModificationException(); |
| lastRet = cursor; |
| cursor = (cursor + 1) & (elements.length - 1); |
| return result; |
| } |
| |
| public void remove() { |
| if (lastRet < 0) |
| throw new IllegalStateException(); |
| if (delete(lastRet)) { // if left-shifted, undo increment in next() |
| cursor = (cursor - 1) & (elements.length - 1); |
| fence = tail; |
| } |
| lastRet = -1; |
| } |
| |
| @Override |
| public void forEachRemaining(Consumer<? super E> action) { |
| Objects.requireNonNull(action); |
| Object[] a = elements; |
| int m = a.length - 1, f = fence, i = cursor; |
| cursor = f; |
| while (i != f) { |
| @SuppressWarnings("unchecked") E e = (E)a[i]; |
| i = (i + 1) & m; |
| // Android-note: This uses a different heuristic for detecting |
| // concurrent modification exceptions than next(). As such, this is a less |
| // precise test. |
| if (e == null) |
| throw new ConcurrentModificationException(); |
| action.accept(e); |
| } |
| } |
| } |
| |
| /** |
| * This class is nearly a mirror-image of DeqIterator, using tail |
| * instead of head for initial cursor, and head instead of tail |
| * for fence. |
| */ |
| private class DescendingIterator implements Iterator<E> { |
| private int cursor = tail; |
| private int fence = head; |
| private int lastRet = -1; |
| |
| public boolean hasNext() { |
| return cursor != fence; |
| } |
| |
| public E next() { |
| if (cursor == fence) |
| throw new NoSuchElementException(); |
| cursor = (cursor - 1) & (elements.length - 1); |
| @SuppressWarnings("unchecked") |
| E result = (E) elements[cursor]; |
| if (head != fence || result == null) |
| throw new ConcurrentModificationException(); |
| lastRet = cursor; |
| return result; |
| } |
| |
| public void remove() { |
| if (lastRet < 0) |
| throw new IllegalStateException(); |
| if (!delete(lastRet)) { |
| cursor = (cursor + 1) & (elements.length - 1); |
| fence = head; |
| } |
| lastRet = -1; |
| } |
| } |
| |
| /** |
| * Returns {@code true} if this deque contains the specified element. |
| * More formally, returns {@code true} if and only if this deque contains |
| * at least one element {@code e} such that {@code o.equals(e)}. |
| * |
| * @param o object to be checked for containment in this deque |
| * @return {@code true} if this deque contains the specified element |
| */ |
| public boolean contains(Object o) { |
| if (o == null) |
| return false; |
| int mask = elements.length - 1; |
| int i = head; |
| Object x; |
| while ( (x = elements[i]) != null) { |
| if (o.equals(x)) |
| return true; |
| i = (i + 1) & mask; |
| } |
| return false; |
| } |
| |
| /** |
| * Removes a single instance of the specified element from this deque. |
| * If the deque does not contain the element, it is unchanged. |
| * More formally, removes the first element {@code e} such that |
| * {@code o.equals(e)} (if such an element exists). |
| * Returns {@code true} if this deque contained the specified element |
| * (or equivalently, if this deque changed as a result of the call). |
| * |
| * <p>This method is equivalent to {@link #removeFirstOccurrence}. |
| * |
| * @param o element to be removed from this deque, if present |
| * @return {@code true} if this deque contained the specified element |
| */ |
| public boolean remove(Object o) { |
| return removeFirstOccurrence(o); |
| } |
| |
| /** |
| * Removes all of the elements from this deque. |
| * The deque will be empty after this call returns. |
| */ |
| public void clear() { |
| int h = head; |
| int t = tail; |
| if (h != t) { // clear all cells |
| head = tail = 0; |
| int i = h; |
| int mask = elements.length - 1; |
| do { |
| elements[i] = null; |
| i = (i + 1) & mask; |
| } while (i != t); |
| } |
| } |
| |
| /** |
| * Returns an array containing all of the elements in this deque |
| * in proper sequence (from first to last element). |
| * |
| * <p>The returned array will be "safe" in that no references to it are |
| * maintained by this deque. (In other words, this method must allocate |
| * a new array). The caller is thus free to modify the returned array. |
| * |
| * <p>This method acts as bridge between array-based and collection-based |
| * APIs. |
| * |
| * @return an array containing all of the elements in this deque |
| */ |
| public Object[] toArray() { |
| final int head = this.head; |
| final int tail = this.tail; |
| boolean wrap = (tail < head); |
| int end = wrap ? tail + elements.length : tail; |
| Object[] a = Arrays.copyOfRange(elements, head, end); |
| if (wrap) |
| System.arraycopy(elements, 0, a, elements.length - head, tail); |
| return a; |
| } |
| |
| /** |
| * Returns an array containing all of the elements in this deque in |
| * proper sequence (from first to last element); the runtime type of the |
| * returned array is that of the specified array. If the deque fits in |
| * the specified array, it is returned therein. Otherwise, a new array |
| * is allocated with the runtime type of the specified array and the |
| * size of this deque. |
| * |
| * <p>If this deque fits in the specified array with room to spare |
| * (i.e., the array has more elements than this deque), the element in |
| * the array immediately following the end of the deque is set to |
| * {@code null}. |
| * |
| * <p>Like the {@link #toArray()} method, this method acts as bridge between |
| * array-based and collection-based APIs. Further, this method allows |
| * precise control over the runtime type of the output array, and may, |
| * under certain circumstances, be used to save allocation costs. |
| * |
| * <p>Suppose {@code x} is a deque known to contain only strings. |
| * The following code can be used to dump the deque into a newly |
| * allocated array of {@code String}: |
| * |
| * <pre> {@code String[] y = x.toArray(new String[0]);}</pre> |
| * |
| * Note that {@code toArray(new Object[0])} is identical in function to |
| * {@code toArray()}. |
| * |
| * @param a the array into which the elements of the deque are to |
| * be stored, if it is big enough; otherwise, a new array of the |
| * same runtime type is allocated for this purpose |
| * @return an array containing all of the elements in this deque |
| * @throws ArrayStoreException if the runtime type of the specified array |
| * is not a supertype of the runtime type of every element in |
| * this deque |
| * @throws NullPointerException if the specified array is null |
| */ |
| @SuppressWarnings("unchecked") |
| public <T> T[] toArray(T[] a) { |
| final int head = this.head; |
| final int tail = this.tail; |
| boolean wrap = (tail < head); |
| int size = (tail - head) + (wrap ? elements.length : 0); |
| int firstLeg = size - (wrap ? tail : 0); |
| int len = a.length; |
| if (size > len) { |
| a = (T[]) Arrays.copyOfRange(elements, head, head + size, |
| a.getClass()); |
| } else { |
| System.arraycopy(elements, head, a, 0, firstLeg); |
| if (size < len) |
| a[size] = null; |
| } |
| if (wrap) |
| System.arraycopy(elements, 0, a, firstLeg, tail); |
| return a; |
| } |
| |
| // *** Object methods *** |
| |
| /** |
| * Returns a copy of this deque. |
| * |
| * @return a copy of this deque |
| */ |
| public ArrayDeque<E> clone() { |
| try { |
| @SuppressWarnings("unchecked") |
| ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); |
| result.elements = Arrays.copyOf(elements, elements.length); |
| return result; |
| } catch (CloneNotSupportedException e) { |
| throw new AssertionError(); |
| } |
| } |
| |
| private static final long serialVersionUID = 2340985798034038923L; |
| |
| /** |
| * Saves this deque to a stream (that is, serializes it). |
| * |
| * @serialData The current size ({@code int}) of the deque, |
| * followed by all of its elements (each an object reference) in |
| * first-to-last order. |
| */ |
| private void writeObject(java.io.ObjectOutputStream s) |
| throws java.io.IOException { |
| s.defaultWriteObject(); |
| |
| // Write out size |
| s.writeInt(size()); |
| |
| // Write out elements in order. |
| int mask = elements.length - 1; |
| for (int i = head; i != tail; i = (i + 1) & mask) |
| s.writeObject(elements[i]); |
| } |
| |
| /** |
| * Reconstitutes this deque from a stream (that is, deserializes it). |
| */ |
| private void readObject(java.io.ObjectInputStream s) |
| throws java.io.IOException, ClassNotFoundException { |
| s.defaultReadObject(); |
| |
| // Read in size and allocate array |
| int size = s.readInt(); |
| allocateElements(size); |
| head = 0; |
| tail = size; |
| |
| // Read in all elements in the proper order. |
| for (int i = 0; i < size; i++) |
| elements[i] = s.readObject(); |
| } |
| } |
